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Maritime Union of New Zealand members at Lyttelton Port's container terminal are back on strike in rolling industrial action over planned roster changes.

Union and port officials held mediation talks on Tuesday and Wednesday after last weekend's scheduled strike was cancelled, although a port spokeswoman confirmed today's two-day action would proceed.

The union has issued strike notices for Jan. 27 and 28 and Feb. 3 through Feb. 5, the latest of which the port is challenging in the Employment Court.

"Our goal is to try and negotiate a settlement soon," port marketing manager Simon Hunt said in a statement on its website. "While we view it as positive that progress is being made in mediated bargaining, we remain disappointed that MUNZ is continuing to issue strike notices during negotiations."

Between 160 and 180 Lyttelton Port employees are part of the Maritime Union covered by the collective contract for the container terminal, which employs more than 250 people. Port management wants to line up work rosters more closely with the company's operating needs.

Port operators across the country have found it difficult to exert greater control over rostering among their unionised workforces, with Ports of Auckland losing a number of contracts in a protracted dispute with the union in 2012.

The existing Lyttelton agreement was set to expire on March 7, 2016, and negotiations for a new collective agreement started in January last year, with 30 meetings in the second half of 2016.

On Dec. 1, union members unanimously voted to go on strike after rejecting a proposal by port management, with the outstanding issues over planned changes the start and finish times for nightshift workers by up to four hours.

In an urgent hearing in the Employment Court last month, Judge Bruce Corkill ordered the union to delay a proposed December strike, which would have a wider impact because the Kaikoura quake boosted volumes going through Lyttelton by an estimated 15 per cent.